Heartworm Disease

Judy Schroeder, DVM   January 11, 2013   Comments Off on Heartworm Disease

A heart infected with heartwormHeartworm disease is caused by a parasitic worm (Dirofilaria immitis) that is transmitted through the bite of an infected mosquito. The adult parasite lives in the heart and pulmonary vessels, and can lead to heart and lung failure, kidney disease, and death if untreated.

Heartworms are found worldwide in temperate and tropical climates and in every state of the US. Certain regions (such as the Southern US) have a much higher incidence of the disease, and there may be local “hot spots” of disease, even in low incidence areas.Map showing incidence of heartworm in the US, 2007Since heartworms are transmitted by mosquitoes, a dog does not need to have direct contact with other dogs to contract the disease. Even an indoor dog could be bitten by a mosquito entering the house. Wild coyotes can also form reservoirs for the disease.  Because people and dogs travel frequently in our country, heartworms can quickly be brought into previously low-incidence areas. (For example, after Hurricane Katrina, many at-risk dogs were adopted out to other parts of the country, including many brought here to Eugene and other Oregon cities.)

Heartworm is best controlled through testing and prevention, since treatment is protracted and expensive. Several different monthly preventatives are available with a prescription. The preventatives work by killing immature stages of the worm before they can mature into adults. It is important to test dogs prior to starting a preventative, since a dog infected with heartworms may experience a severe reaction to the preventative.

Due to the unpredictability of heartworm disease and the potentially devastating consequences, we strongly recommend that all dogs be given a monthly preventative year-round. Many of these products also help prevent fleas, roundworms, and hookworms, so there are multiple benefits. Dogs 6 months of age or older should be tested before starting a preventative, and retested at least every 2 years, depending on lifestyle. We can help you decide which preventative is best for your dog.

More information about heartworm  prevention and treatment is available through the American Heartworm Society.